African Milk Barrel

Euphorbia horrida is endemic to the Eastern Cape and Western Cape Provinces of South Africa.

• Found in the area around Uitenhage, Port Elizabeth, and the Sundays River Valley in the Eastern Cape
• Extends westward into parts of the Western Cape
• Occurs at elevations of approximately 100 to 600 meters
• Grows on rocky hillsides, exposed ridges, and gravelly flats in Albany Thicket and Eastern Valley Bushveld vegetation types
• The region receives 400 to 600 mm of annual rainfall distributed throughout the year
• First described by the German-born South African botanist Johann Heinrich Friedrich Link in 1830
• The Eastern Cape is one of the world's great centers of succulent plant diversity
• Several varieties are recognized, differing in spine color, stem size, and growth habit

A large, clump-forming, columnar succulent with a strikingly cactus-like appearance.

Stems:
• Erect, cylindrical to slightly club-shaped, branching from the base to form large clumps
• Individual stems 8 to 15 cm in diameter, reaching 30 to 100 cm tall (occasionally taller in habitat)
• Deeply ribbed with 10 to 15 prominent, wavy ribs running vertically along the stem
• Stem color dark green to grayish-green, sometimes with a glaucous bloom
• Older stems may develop a woody, corky base

Spines:
• Formidable, rigid, and sharp — the plant's most distinctive feature
• Solitary or in groups of 2 to 3 at each areole-like tubercle along the ribs
• Spines 10 to 40 mm long, stout, varying from reddish-brown to gray or nearly black
• Persistent and extremely sharp — capable of piercing leather gloves
• Not true spines but modified peduncles (flower stalk remnants) that have become woody and hardened

Leaves:
• Tiny, rudimentary, scale-like, 1 to 3 mm long
• Deciduous, present only briefly on new growth
• Practically invisible amid the formidable spines

Flowers:
• Small, cyathia (the characteristic Euphorbia inflorescence) — not showy like true cactus flowers
• Yellowish-green, 5 to 8 mm in diameter, produced near the stem tips in summer
• Each cyathium consists of a single female flower surrounded by several male flowers within a cup-like involucre
• Produces small, three-lobed capsules

Latex:
• Copious, white, milky latex from all wounded tissues
• Highly toxic and caustic

A robust xerophyte adapted to the semi-arid conditions of the Eastern Cape.

Habitat:
• Rocky hillsides, exposed ridges, and gravelly slopes in Albany Thicket vegetation
• Often found growing among rocks and boulders that provide some root-zone protection
• Tolerates full sun and reflected heat
• Associated with other succulents including Aloes, Crassulas, and Stapeliads

Adaptations:
• The thick, ribbed stems store large quantities of water for survival during dry periods
• The ribs allow the stem to expand and contract dramatically as water is stored or depleted
• Formidable spines deter all but the most determined herbivores
• CAM photosynthesis maximizes water-use efficiency
• The toxic latex provides a secondary chemical defense against herbivory and microbial infection

Reproduction:
• Pollinated by small insects, particularly bees and flies attracted to the nectar glands of the cyathia
• Seeds are dispersed ballistically — the ripe capsule explodes, flinging seeds up to 3 meters from the parent plant
• Also reproduces vegetatively by basal branching and offset formation
• Plants can form extensive clumps over many decades

All parts of Euphorbia horrida contain highly toxic, caustic milky latex.

Toxic Compounds:
• The latex contains potent diterpene esters, including ingenol and related compounds
• These are powerful inflammatory agents and tumor promoters

Effects on Humans:
• Skin contact: causes severe burning, redness, blistering, and contact dermatitis that may persist for days
• Eye contact: extremely dangerous — can cause severe corneal damage, conjunctivitis, and potential permanent vision impairment
• Ingestion: causes burning of the mouth and throat, nausea, vomiting, and gastrointestinal distress
• The spines can cause mechanical injury independent of the latex toxicity

Safety Precautions:
• Always wear thick gloves, long sleeves, and eye protection when handling or pruning
• Use caution when working near the plant — spine puncture wounds can inject latex under the skin
• Keep away from children and pets
• If latex contacts skin, wash immediately with soap and water

A hardy and dramatic succulent that is relatively easy to grow, provided its need for excellent drainage is met.

Soil:
• Extremely well-draining, mineral-rich mix — use 80 to 90% inorganic material (pumice, perlite, coarse sand, gravel)
• The plant is adapted to rocky, nutrient-poor substrates
• Good drainage is absolutely critical to prevent root rot

Light:
• Full sun to very bright light — at least 6 hours of direct sunlight daily for best form and spine development
• Tolerates partial shade but may become etiolated and lose its compact shape
• The thick stems are adapted to intense sunlight and heat

Water:
• Water moderately during the active growing season (spring to autumn), allowing the soil to dry completely between waterings
• Reduce to minimal watering in winter during the rest period
• Overwatering will cause root rot and stem splitting
• The plant can survive extended drought with no ill effects

Temperature:
• Prefers warm to hot conditions (20 to 35°C) during the growing season
• Tolerates cool winter temperatures down to approximately 0°C if kept completely dry
• Good air circulation helps prevent fungal and bacterial problems

Propagation:
• Most commonly propagated from seed, which germinates readily in warm, sandy conditions
• Stem cuttings can also be used — cut with a clean blade, rinse off latex, and allow to callus for 7 to 10 days before planting in dry soil
• Always wear protective equipment when handling cuttings due to toxic latex